98 Krug von Nidcla oil the Mineral Springs of Iceland. 



are subject to small eruptions at regular periods. The largest, 

 generally called the Small Strokr, breaks out at intervals of from 

 twenty-five to thirty minutes; large masses of vapour then 

 stream from its mouth, and carry the water with them to a 

 height of from eight to ten feet. Such an eruption lasts about 

 thirty seconds, and then perfect tranquillity is restored. There 

 are also very many springs whose surface is never agitated, 

 either by a continued or a sudden evolution of vapour. Their 

 temperature is always more or less under the boiling point. 



The regular periods at which the eruptions of the Geyser and 

 of all intermitting'springs are repeated, impart to them the cha- 

 racter of the action of an artificial machine. We cannot suppose 

 the existence of a system of valves, for Nature always employs 

 the simplest means to produce her most remarkable phenomena. 

 If we group together the phenomena of the Geyser and other 

 intermitting springs, we can deduce some conclusions regarding 

 the development of such immense energy as that exhibited by 

 the Geyser and the Strokr, which may be of importance not only 

 for the theory of all intermitting springs, but also of volcanos. 

 For what are volcanoes but intermitting springs of melted 

 earth ? As to the agency which raises the water of the Geyser 

 to so extraordinary a height, no doubt can exist. It is gaseous 

 bodies, chiefly steam, whose expansive power can be immeasur- 

 ably increased by an elevation of temperature. 



The temperature of the thermal springs at their surface can- 

 not exceed 80 R. (212 K), on account of the continued evapo- 

 ration under the pressure of the atmosphere. It even sinks 

 considerably in most springs, as in the Geyser, during periods of 

 repose. But that the temperature in the deeper portions of the 

 water-column must be much higtter than in the upper, is evi- 

 dent from the evolution which takes place there of steam: whose 

 expansive power stands in equilibrium with the common pressure 

 of the atmosphere, and of the superior portions of the water.* 



Warm springs may be divided into three classes : 



1. Those that are constantly agitated and in a boiling- state 

 (permanent thermal springs). 



* We find it stated in a late number of the Comptes Rendus of the French 

 Academy of Sciences, that M. Lattin, during a recent expedition to Iceland, 

 ascertained that the temperature of the Great Geyser, at a depth of 60 feet, 

 was 255 Fahr. ; and that of the Strokr, at a depth of 40 feet, 233 Fahr. ED. 



